public class 自己实现字符串大写转小写 {
        public String toLowerCase(String s){
            StringBuilder sb = new StringBuilder();

            for(int i = 0;i < s.length();i ++){
                char ch = s.charAt(i);
                if (Character.isLetter(ch)){
                    if(Character.isLowerCase(ch)){
                        ch = (char)(ch +32);
                    }
                }
            }
        }
}
